This invention relates to polyamide compositions useful as hot-melt adhesives.
One important property of adhesive compositions is their "open assembly time" or "open time". Open time is the maximum time a hot melt coated surface may be allowed to cool before bonding and still retain satisfactory adhesion. The open time required of a polyamide adhesive depends on the specific applications and can vary, for commercially available polyamide adhesives, from less than five seconds to about fifty-five seconds.
There are many disclosures in the art relating to polyamide compositions having hot-melt adhesive properties and the methods for preparing such compositions. A poly(ester-amide) adhesive composition having a long open assembly time is disclosed in U.S. Pat. No. 4,485,233. This patent disclosed poly(ester-amide) adhesive compositions comprising the product of polymerization of (a) from 10 to 60 equivalent percent of a polymeric fatty acid, and (b) from 40 to 90 equivalent percent of a dicarboxylic acid, with a substantially equivalent amount of (c) from 40 to 90 equivalent percent of an organic diamine and (d) from 10 to 60 equivalent percent of a diol. The organic diamine component (c) may comprise a linear aliphatic, cycloaliphatic or aromatic diamine, and, disclosed as the preferred diamines, are piperazine, 1,3-dipiperidyl propane and diamines with an odd number of carbon atoms such as 1,3-diaminopropane.
Representative of other prior art adhesive compositions are those described in U.S. Pat. Nos. 3,377,303 and 3,444,026. The latter compositions comprise the reaction product of a dimer fatty acid and a wide variety of diamines. Copolymerizing dicarboxylic acids, including aliphatic dicarboxylic acids such as adipic, sebacic and azelaic acids, are also disclosed as components of the adhesive compositions.
Polyamide compositions useful as hot-melt adhesives for adhering vinyl plastics are also disclosed in U.S. Pat. No. 3,847,875. The latter compositions are the reaction product of 1,8 or 1,9-heptadecane dicarboxylic acid and specific heterocyclic diamines such as piperazine. Copolymerizable dicarboxylic acids such as azelaic, sebacic and adipic acids are also disclosed as components of the adhesives.
It has been extremely difficult to obtain an adhesive formulation capable of exhibiting both a long open time and excellent ultimate bond strength. Generally, adhesives exhibiting long open time have not exhibited high bond strengths, and adhesives exhibiting high bond strengths have not exhibited long open times. It is, therefore, a goal of those skilled in the art to obtain an adhesive formulation which exhibits long open time and which also preferably exhibits excellent bond strength.